Object Mentor Blog: Testing GUIs Part I: RoR.

Testing GUIs Part I: RoR.

Uncle Bob — Sat, 13 Jan 2007 17:24:00 +0000

Testing GUIs is one of the the holy grails of Test Driven Develoment (TDD). Many teams who have adopted TDD for other parts of their projects have, for one reason or another, been unable to adequately test the GUI portion of their code.

In this series of article I will show that GUI testing is a solved problem. Over the years the TDD community has produced and accumulated tools, frameworks, libraries, and techniques that allow any team to test their GUI code as fully as any other part of their code.

Testing GUIs Part I: Ruby on Rails

In the world of web development, no community has solved the problem of GUI testing better than the Ruby on Rails community. When you work on a rails project, testing the GUI is simply de-rigeur. The rails framework provides all the necessary tools and access points for testing all aspects of the application, including the generation of HTML and the structure of the resulting web pages.

Web pages in rails are specified by .rhtml files that contain a mixture of HTML and ruby code similar to the way Java and HTML are mixed in .jsp files. The difference is that .rhtml files are translated at runtime rather than being compiled into servlets the way .jsp pages are. This makes it very easy for the rails environment to generate the HTML for a web page outside of the web container. Indeed, the web server does not need to be running.

This ease and portability of generating HTML means that the rails test framework merely needs to set up the variables needed by the ruby scriptlets within the .rhtml files, generate the HTML, and then parse that HTML into a form that the tests can query.

A typical example.

The tests query the HTML using an xpath-like syntax coupled with a suite of very powerful assertion functions. The best way to understand this is to see it. So here is a simple file named: autocomplete_teacher.rhtml.

<ul class="autocomplete_list"> 
<% @autocompleted_teachers.each do |t| %> 
<li class="autocomplete_item"><%= "#{create_name_adornment(t)} #{t.last_name}, #{t.first_name}"%></li> 
<% end %> 
</ul>

You don’t have to be a ruby programmer to understand this. All it is doing is building an HTML list. The Ruby scriptlet between <% and %> tokens simple loops for each teacher creating an <li> tag from an “adornment”, and the first and last name. (The adornment happens to be the database id of the teacher in parentheses.) A simple test for this .rhtml file is:

  def test_autocomplete_teacher_finds_one_in_first_name
    post :autocomplete_teacher, :request=>{:teacher=>"B"}
    assert_template "autocomplete_teacher" 
    assert_response :success
    assert_select "ul.autocomplete_list" do
      assert_select "li.autocomplete_item", :count => 1
      assert_select "li", "(1) Martin, Bob" 
    end
  end

The post statement simply invokes the controller that would normally be invoked by a POST url of the form: POST /teachers/autocomplete_teacher with the teacher parameter set to "B".
The first assertion makes sure that the controller rendered the autocomplete_teacher.rhtml template.
The next makes sure that the controller returned success.
the third is a compound assertion that starts by finding the <ul> tag with a class="autocomplete_list" attribute. (Notice the use of css syntax.)
- Within this tag there should be an <li> tag with a class="autocomplete_item" attribute,
- and containing the text (1) Martin, Bob.

It should not come as any surprise that this test runs in a test environment in which the database has been pre-loaded with very specific data. For example, this test database always has “Bob Martin” being the first row (id=1) in the Teacher table.

The assert_select function is very powerful, and allows you to query large and complex HTML documents with surgical precision. Although this example give you just a glimpse of that power, you should be able to see that the rails testing scheme allows you to test that all the scriptlets in an .rhtml file are behaving correctly, and are correctly extracting data from the variables set by the controller.

An example using RSpec and Behavior Driven Design.

What follows is a more significant rails example that uses an alternate testing syntax known as Behavior Driven Design (BDD). The tool that accepts this syntax is called RSpec.

Imagine that we have a page that records telephone messages taken from teachers at different schools. Part of that page might have an .rhtml syntax that looks like this:

<h1>Message List</h1>

<table id="list">
  <tr class="list_header_row">
    <th class="list_header">Time</th>
    <th class="list_header">Caller</th>
    <th class="list_header">School</th>
    <th class="list_header">IEP</th>
  </tr>
<%time_chooser = TimeChooser.new%> 
<% for message in @messages %>
  <%cell_class = cycle("list_content_even", "list_content_odd")%>
  <tr id="list_content_row">
    <td id="time"   class="<%=cell_class%>"><%=h(time_chooser.format_time(message.time)) %></td>
    <td id="caller" class="<%=cell_class%>"><%=h person_name(message.caller) %></td>
    <td id="school" class="<%=cell_class%>"><%=h message.school.name %></td>
    <td id="iep"    class="<%=cell_class%>"><%=h (message.iep ? "X" : "") %></td>
  </tr>
<% end %>
</table>

Clearly each message has a time, caller, school, and some kind of boolean field named “IEP”. We can test this .rhtml file with the following RSpec specification:

context "Given a request to render message/list with one message the page" do
  setup do
    m = mock "message" 
    caller = mock "person",:null_object=>true
    school = mock "school" 

    m.should_receive(:school).and_return(school)
    m.should_receive(:time).and_return(Time.parse("1/1/06"))
    m.should_receive(:caller).any_number_of_times.and_return(caller)
    m.should_receive(:iep).and_return(true)

    caller.should_receive(:first_name).and_return("Bob")
    caller.should_receive(:last_name).and_return("Martin")

    school.should_receive(:name).and_return("Jefferson")
    assigns[:messages]=[m]

    assigns[:message_pages] = mock "message_pages", :null_object=>true
    render 'message/list'
  end

  specify "should show the time" do
    response.should_have_tag :td, :content=>"12:00 AM 1/1", :attributes=>{:id=>"time"}
  end

  specify "should show caller first and last name" do
    response.should_have_tag :td, :content=>"Bob Martin", :attributes=>{:id=>"caller"}
  end

  specify "should show school name" do
    response.should_have_tag :td, :content=>"Jefferson", :attributes=>{:id=>"school"}
  end

  specify "should show the IEP field" do
    response.should_have_tag :td, :content=>"X",:attributes=>{:id=>"iep"}
  end
end

I’m not going to explain the setup function containing all that mock stuff you see at the start. Let me just say that the mocking facilities of RSpec are both powerful and convenient. Actually you shouldn’t have too much trouble understanding the setup if you try; but understanding it is not essential for this example. The interesting testing is in the specify blocks.

You shouldn’t have too much trouble reading the specify blocks. You can understand all of them if you understand the first. Here is what it does:

The first spec ensures that <td id="time">12:00 AM 1/1</td> exists in the HTML document. This is not a string compare. Rather it is a semantic equivalence. Whitespace, and other attributes and complications are ignored. This spec will pass as long as there is a td tag with the appropriate id and contents.

HTML Testing Discipline and Strategy

One of the reasons that GUI testing has been so problematic in the .jsp world is that the java scriptlets in those files often reach out into the overall application domain and touch code that ties them to the web container and the application server. For example, if you make a call from a .jsp page to a database gateway, or an entity bean, or some other structure that is tied to the database; then in order to test the .jsp you have to have the full enabling context running. Rails gets away with this because the enabling context is lightweight, portable, and disconnected from the web container, and the live database. Even so, rails applications are not always as decoupled as they should be.

In Rails, Java, or any other web context, the discipline should be to make sure that none of the scriptlets in the .jsp, .rhtml, etc. files know anything at all about the rest of the application. Rather, the controller code should load up data into simple objects and pass them to the scriptlets (typically in the attributes field of the HttpServletRequest object or its equivalent). The scriptlets can fiddle with the format of this data (e.g. data formats, money formats, etc.) but should not do any calculation, querying, or other business rule or database processing. Nor should the scriptlets navigate through the model objects or entities. Rather the controller should do all the navigating, gathering, and calculating and present the data to the scriptlets in a nice little package.

If you follow this simple design discipline, then your web pages can be generated completely outside of the web environment, and your tests can parse and inspect the html in a simple and friendly environment.

Conclusion

I’ll have more to say about RSpec in a future blog. BDD is an exciting twist on the syntax of testing, that has an effect far greater than the simple syntax shift would imply.

I hope this article has convinced you that the rails community has solved the problem of testing HTML generation. This solution can be easily extrapolated back to Java and .NET as future blogs in this series will show.

Clearly the problem of testing Javascript, and the ever more complex issues of Web2.0 and GTK are not addressed by this scheme. However, there are solutions for Javascript that we will investigate in future blogs in this series.

Finally, this technique does not test the integration and workflow of a whole application. Again, those are topics for later blogs.

I hope this kickoff blog has been informative. If you have a comment, question, or even a rant, please don’t hesitate to add a comment to this blog.

"Testing GUIs Part I: RoR." by prudhvi@30gigs.com

Tue, 17 Jul 2007 02:31:52 +0000

I am a newbie to Ruby. I am interested in testing the url’s placed in a web-page to find the ‘Page not Found’ error in specific and other link issues like passing the required params in generic using Ruby.

Could you pl guide me on the aforementioned. Maybe through some pdf and examples.

Regards, Prudhvi

"Testing GUIs Part I: RoR." by Aaron

Wed, 31 Jan 2007 02:36:15 +0000

It is informative, and it is the most effective way I can find as well. Actually I am just finding a solution to develop a better java testing tool to help my team to test faster, easier and in better efficiency. The best idea seems to use annotations and xml configurations to decorate test cases. A typical framework of this kind is TestNG. It seems the advantages of this kind of testing framework is:

1> Stronger control in the workflow of test cases running. You can either use specific annotation syntax to put them into groups, or identify some executing sequences. 2> More flexible. Testing classes don’t have to extend some base classes as JUnit, or have some rules to restrict method defining. 3> Accelerate procedure of developing test cases in some specific situations.

Aha, this is not bad comparing with JUnit. But if it comes to rails, annotation kind of things would not be that competent. Because using syntax way to test, it must be much more flexible & powerful.

"Testing GUIs Part I: RoR." by Andy Dent

Wed, 24 Jan 2007 03:18:16 +0000

GUI testing is a solved problem

Uhh, do you just mean HTML Forms Web App GUI testing is a solved problem or is your series going to include

rich internet apps using Flash
desktop apps
mobile apps?

I’m really hoping for a good answer on desktop apps because, surprisingly, there’s still a lot of work happening developing them, both for retail and inhouse. We could really use a good solution for wxPython-based GUIs!

"Testing GUIs Part I: RoR." by David Chelimsky

Sun, 14 Jan 2007 08:49:38 +0000

Anthony – yes, RSpec on Rails already unofficially supports assert_select for tags (not yet for rjs). If you are using the 0.7.5 plugin, take a look at spec/expecations/should_have_spec.rb to see what you can do. We used should_have because should_select doesn’t talk about the behaviour of the system under test. It sounds more like the behaviour of rspec, which “should_select” or “should_find” an element. What we’re saying is that the response should have some material in it, so “should_have” makes sense to me.

At this point there are several things holding me back from making it officially supported. For one, the syntax is likely to change subtly. We also need to support rjs. And the error messages are completely useless. Right now we’re just wrapping assert_select, and its error messages just say “expected 1 element(s), found 0”. That is not all that helpful to me.

Once these are resolved, we’ll make it official. In the mean time you are free to use what’s there – just be aware that there will be some API changes and you’ll have to change your specs for a future release.

"Testing GUIs Part I: RoR." by Uncle Bob

Sun, 14 Jan 2007 08:13:10 +0000

Anthony,

Yes, I plan on discussing the testing of thick client GUIs, and GUIs with lots of JavaScript.

"Testing GUIs Part I: RoR." by Anthony Bailey

Sun, 14 Jan 2007 02:09:05 +0000

Thanks for the article,

(I assume RSpec plans to support some kind of should_css_select equivalent to the elegant assert_select sometime soon. It’s already distressing to go back to the noisier tag style assertions.)

Will you be discussing the testing of direct manipulation (e.g. mouse-driven inputs, highly graphical output) user interfaces at all? I have found those to be the ones where automated testing is the most difficult, although not impossible with the right kind of intermediate representations in place.

"Testing GUIs Part I: RoR." by David Chelimsky

Sun, 14 Jan 2007 00:04:28 +0000

Very happy to see that you’re enjoying using RSpec.

There are some things that I’ve started to approach differently. I posted on this next door and would love to get your feedback.